1 /* $OpenBSD: arc4random.h,v 1.4 2015/01/15 06:57:18 deraadt Exp $ */
2
3 /*
4 * Copyright (c) 1996, David Mazieres <dm@uun.org>
5 * Copyright (c) 2008, Damien Miller <djm@openbsd.org>
6 * Copyright (c) 2013, Markus Friedl <markus@openbsd.org>
7 * Copyright (c) 2014, Theo de Raadt <deraadt@openbsd.org>
8 *
9 * Permission to use, copy, modify, and distribute this software for any
10 * purpose with or without fee is hereby granted, provided that the above
11 * copyright notice and this permission notice appear in all copies.
12 *
13 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
14 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
15 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
16 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
17 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
18 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
19 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
20 */
21
22 /*
23 * Stub functions for portability.
24 */
25 #include <sys/elf.h>
26 #include <sys/endian.h>
27 #include <sys/mman.h>
28 #if ARC4RANDOM_FXRNG != 0
29 #include <sys/time.h> /* for sys/vdso.h only. */
30 #include <sys/vdso.h>
31 #include <machine/atomic.h>
32 #endif
33
34 #include <err.h>
35 #include <errno.h>
36 #include <signal.h>
37 #include <stdbool.h>
38 #include <stdint.h>
39
40 #if ARC4RANDOM_FXRNG != 0
41 /*
42 * The kernel root seed version is a 64-bit counter, but we truncate it to a
43 * 32-bit value in userspace for the convenience of 32-bit platforms. 32-bit
44 * rollover is not possible with the current reseed interval (1 hour at limit)
45 * without dynamic addition of new random devices (which also force a reseed in
46 * the FXRNG design). We don't have any dynamic device mechanism at this
47 * time, and anyway something else is very wrong if billions of new devices are
48 * being added.
49 *
50 * As is, it takes roughly 456,000 years of runtime to overflow the 32-bit
51 * version.
52 */
53 #define fxrng_load_acq_generation(x) atomic_load_acq_32(x)
54 static struct vdso_fxrng_generation_1 *vdso_fxrngp;
55 #endif
56
57 static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER;
58 #define _ARC4_LOCK() \
59 do { \
60 if (__isthreaded) \
61 _pthread_mutex_lock(&arc4random_mtx); \
62 } while (0)
63
64 #define _ARC4_UNLOCK() \
65 do { \
66 if (__isthreaded) \
67 _pthread_mutex_unlock(&arc4random_mtx); \
68 } while (0)
69
70 static inline void
_getentropy_fail(void)71 _getentropy_fail(void)
72 {
73 raise(SIGKILL);
74 }
75
76 static inline void
_rs_initialize_fxrng(void)77 _rs_initialize_fxrng(void)
78 {
79 #if ARC4RANDOM_FXRNG != 0
80 struct vdso_fxrng_generation_1 *fxrngp;
81 int error;
82
83 error = _elf_aux_info(AT_FXRNG, &fxrngp, sizeof(fxrngp));
84 if (error != 0) {
85 /*
86 * New userspace on an old or !RANDOM_FENESTRASX kernel; or an
87 * arch that does not have a VDSO page.
88 */
89 return;
90 }
91
92 /* Old userspace on newer kernel. */
93 if (fxrngp->fx_vdso_version != VDSO_FXRNG_VER_1)
94 return;
95
96 vdso_fxrngp = fxrngp;
97 #endif
98 }
99
100 static inline int
_rs_allocate(struct _rs ** rsp,struct _rsx ** rsxp)101 _rs_allocate(struct _rs **rsp, struct _rsx **rsxp)
102 {
103 struct {
104 struct _rs rs;
105 struct _rsx rsx;
106 } *p;
107
108 if ((p = mmap(NULL, sizeof(*p), PROT_READ|PROT_WRITE,
109 MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED)
110 return (-1);
111 /* Allow bootstrapping arc4random.c on Linux/macOS */
112 #ifdef INHERIT_ZERO
113 if (minherit(p, sizeof(*p), INHERIT_ZERO) == -1) {
114 munmap(p, sizeof(*p));
115 return (-1);
116 }
117 #endif
118
119 _rs_initialize_fxrng();
120
121 *rsp = &p->rs;
122 *rsxp = &p->rsx;
123 return (0);
124 }
125
126 /*
127 * This isn't only detecting fork. We're also using the existing callback from
128 * _rs_stir_if_needed() to force arc4random(3) to reseed if the fenestrasX root
129 * seed version has changed. (That is, the root random(4) has reseeded from
130 * pooled entropy.)
131 */
132 static inline void
_rs_forkdetect(void)133 _rs_forkdetect(void)
134 {
135 /* Detect fork (minherit(2) INHERIT_ZERO). */
136 if (__predict_false(rs == NULL || rsx == NULL))
137 return;
138 #if ARC4RANDOM_FXRNG != 0
139 /* If present, detect kernel FenestrasX seed version change. */
140 if (vdso_fxrngp == NULL)
141 return;
142 if (__predict_true(rsx->rs_seed_generation ==
143 fxrng_load_acq_generation(&vdso_fxrngp->fx_generation32)))
144 return;
145 #endif
146 /* Invalidate rs_buf to force "stir" (reseed). */
147 memset(rs, 0, sizeof(*rs));
148 }
149